Steering shaft assemblies for automobiles commonly employ steering shafts for collapsible telescoping movement upon encountering a collapsing force. Providing a steering shaft assembly that can collapse helps to minimize injury to a driver of a vehicle when involved in an accident. To achieve telescoping movement between related steering shaft assembly components, typically a tubular main body is joined to a solid shaft utilizing an injection molding process.
To utilize an injection molding process to join the tubular main body to the solid shaft, holes are typically formed in a wall of the tubular main body and in the shaft. Upon injecting the plastic through the respective holes of the tubular main and the shaft, a plastic shear pin or pins formed by the injection molding maintains the main body and the shaft in an axially fixed relation to one another until a collapsing force is encountered of sufficient magnitude to shear the pin(s). Although effective, this approach is labor intensive and costly.
Another known method utilized to fix a tubular main body to a solid shaft is through the use of leaf springs inserted between an inner surface of the main body and an outer surface of the shaft. The leaf springs are formed with a ridge extending longitudinally along the length thereof so that when the leaf springs are inserted between the shaft and the main body, the ridge makes linear contact along the length of the main body to impart a radial load between the shaft and the main body. The leaf springs provide a metal-to-metal contact between the shaft and the main body, and thus, grease is commonly used to ensure proper telescoping movement upon encountering a collapsing force between the shaft and the main body.
With the ridges of the springs traversing between the shaft and the main body in an axial direction, “lash” may result between the shaft and the main body. “Lash” is the term given when relative torsional movement is present between mating steering shaft components, such as between the shaft and the main body. “Lash” is extremely undesirable in a steering shaft assembly, as it reduces the response time of the wheels turning on a vehicle in response to a driver turning a hand wheel connected to the steering shaft assembly. To assist in reducing the amount of “lash” utilizing leaf springs having longitudinally extending ridges, the shaft and main body are typically formed having mating hexagonal shapes. Having to form the shaft and main body in mating hexagonal shapes adds cost to the manufacture of steering shaft assemblies. In addition, the requirement for grease adds cost and inconvenience to the manufacturing process.